The present invention relates to a retractable sensor holder for immersion-type and flow-type measuring systems, and in particular to a retractable sensor holder that provides an effective cleaning and/or sterilization path for wetted parts of the sensor and sensor holder, while providing substantially flush mounting with the vessel wall.
The pharmaceutical and biotechnology markets employ sensitive processes that require analytical sensors to be mounted in sterile environments. Typically, these environments are closed vessels, wherein fermentation and cell growth cycles can last from a few days to several months. The analytical sensors, for example pH sensors, are sensitive devices that can be affected by the conditions experienced inside the vessels, and must be maintained correctly to ensure adequate performance. Fouling from proteins will cause drift and biomass penetrating the electrode reference system will over time cause some offsets. Harsh cleaning cycles that would otherwise destroy pH electrodes require users to manually remove them prior to commencing with vessel cleaning.
Conformance to specific industry standards is often required to ensure the proper cleaning and sterilization of the vessels and the sensors. For example, ASME Bioprocessing standard 1997 and 3-A recommendations (xe2x80x9cthe 3A Standardsxe2x80x9d), which are incorporated herein by reference for all purposes, have been developed by/for producers of meat, milk and eggs and are still the standards by which most food and beverage producers gage their equipment for suitability. Meat, milk and eggs are considered to be xe2x80x9cworst casexe2x80x9d for bacterial growth. If equipment follows the standards for these products, then producers properly using the equipment can be assured that the equipment will not add to their bacterial problems. Producers of other foods with less bacterial risk may thus choose how much of the standards to employ based upon what they feel they need. However, some users may ask for even further requirements, such as better surface finishes, etc.
In general, the 3A Standards assume that equipment will meet sanitation requirements by at least one of two methods (even though some users will demand both): xe2x80x9cmechanical cleaningxe2x80x9d (often called by users as xe2x80x9cclean-in-placexe2x80x9d or xe2x80x9cCIPxe2x80x9d), and xe2x80x9cremovable for cleaning.xe2x80x9d In the latter case, equipment must be easily removable (i.e., require no tools to remove) so that an operator or quality assurance or regulatory inspector can routinely pull out sensors, inspect them for cleanliness, and clean them if necessary, before re-inserting them into the process. In the case of mechanical cleaning, the idea is that procedures carried out within the process itself can clean the installed sensorsxe2x80x94with no need to pull them out. In general, this method requires such things as very smooth surface finishes and no acute angle corners (e.g., angles no less than 135 degrees) where material can build up or where flowing cleaning fluids cannot carry buildup away. Further, using the mechanical cleaning method, the equipment must be able to withstand the process and protect the integrity of the sealed, cleaned process system. For example, it is routine after a food or fermentation batch to clean the system before starting a new batch of similar or different product. To this end, a typical method might be to follow a product batch with hot water, then a caustic solution, then hot water, then a steam-sterilization, and then let the sealed system cool down (which creates a vacuum situation).
Regardless of which method is employed, under the 3A Standards anytime a xe2x80x9csealxe2x80x9d is exposed to the process it must be an O-ring (i.e., not a flat gasket) that is acceptable for contact with food and it must be removable/replaceable by the operator each time the sensor is removed/replaced. Furthermore, all other materials of construction must be acceptable for contact with food, normally stainless steel (300 series or better) or TEFLON(trademark). FDA approved food contact materials are listed in Title 21 of the United States Code of Federal Regulations (xe2x80x9c21 CFRxe2x80x9d), which is incorporated herein by reference for all purposes. Additionally, ASME BPE1997, which is also incorporated herein by reference for all purposes, sets out requirements for easy to clean tank and process connections. It is also noted that there are alternative sanitary standards being developed which seek not to assume cleanliness based upon theoretical design guidelines like the 3A Standards, but rather to actually test equipment with introduction of bacteria and media, cleaning, retesting, etc.
FIG. 1 shows a typical prior art 25 mm process connection or weld spud 1. The historical approach to meeting the various sanitary requirements has become known as the 25 mm side port coupling or 25 mm weld spud, and is commonly used today for pH and dissolved oxygen sensors. The 25 mm weld spud 1 is generally tubularly shaped. In this approach, a xe2x80x9cstationaryxe2x80x9d sensor (not shown) is mounted to a tank wall 2 via the 25 mm weld spud 1. The sensor is held in place within the 25 mm weld spud 1 by a thread coupling 4. The sensor is outfitted with an O-ring that forms a fluid tight seal between the sensor and the inside of the 25 mm weld spud 1. With the sensor mounted in the 25 mm weld spud 1, the sensor will typically be steam sterilized at the same time as the inside of the tank. When maintenance is required, the sensor can be removed from the port by disengaging the quick disconnect fitting or unscrewing the coupling nut, respectively. After the sensor is removed, it can then be cleaned and recalibrated or replaced, if necessary. Once maintenance is completed, the sensor is returned to the 25 mm weld spud 1. The entire tank then undergoes sterilization to ensure that no foreign organisms were inadvertently introduced during the sensor maintenance. However, this approach has some obvious limitations, including: (1) maintenance can only be carried out while the vessel is empty; (2) sensors must be handled and maintained manually; and (3) after maintenance the entire tank needs to be re-sterilized. Moreover, because the generally tubular 25 mm weld spud 1 extends away from the inside of the tank, the interior 3 of the 25 mm weld spud 1 cannot be adequately reached by steam for sterilization and for cleaning.
In order to provide more flexibility to users, the concept of xe2x80x9cretractablexe2x80x9d sensor holders emerged some years ago. The idea was to be able to retract the sensor from the vessel and isolate it from the tank without having to interrupt the process. Maintenance could then be carried out on the sensor while the process continued to run. The object has been to design retractable holders that would fit onto the existing process connections. To this end, many unsuccessful attempts have been made to use the de facto standard 25 mm weld spud in conjunction with sanitary retractable holders. These too have not been successful primarily because not all wetted parts can be adequately reached by steam for sterilization. For example, FIG. 2 shows a typical prior art retractable holder 12 in a retracted, cleaning position.
The retractable holder 12 includes a stationary portion 5 and a movable portion 6 which holds a sensor 14. The stationary portion 5 is connected to a vessel 16 (such as, for example, a tank) by a 25 mm weld spud 18. In the retracted position, a front cap 20 provides a substantially flush mount with the inside surface 26 of the vessel 16, and isolates the inside of the retractable holder 12 and the sensor 14 from the inside of the vessel 16. A cleaner inlet 22 and a cleaner outlet 24 are provided in the retractable holder 12 to introduce cleaning and/or sterilization agents to clean the sensor 14 and the interior of the retractable holder 12. A pair of O-rings 8, 10 are placed between the stationary portion 5 and the movable portion 6 to provide a fluid tight seal. The design provides a substantially flush, cleanable mount with the inside surface 26 of the vessel 16 that facilitates vessel cleaning. However, the cleaning of the sensor 14 and the interior of the holder 12 is still problematic. First, the area between the two O-rings 8, 10 cannot be effectively reached during the cleaning process. Also, the diameters of analytical sensors, for example pH electrode sensors, can typically be 12 mm and the inside diameter of the port adapter is only 25 mm. During cleaning, all internal surfaces and seals must be adequately contacted by cleaning agent with sufficient velocity. But channel 28 (the space between the stationary part and the moving part of the retractable holder 12) is impracticably narrow. The cleaning agent takes the path of least resistance and flows between the inlet 22 and the outlet 24 with insufficient velocity of the cleaner in the channel 28. The end result is poor cleaning of the sensor 14 and the area immediately behind the front cap 20. During sterilization, for example with steam, the same problems are evident. Steam sterilization is typically performed at 120-130xc2x0 C. for approximately one hour. With steam, the situation is further complicated because steam condensate can become trapped in the area immediately behind the front cap 20, making it difficult to raise the chamber temperature to the required level for effective sterilization.
Alternative designs have been attempted to solve some of the foregoing problems, for example the INTRAC(copyright) brand 777-SL Retractable Housing from Mettler-Toledo Process Analytical, Inc. of Wilmington, Mass. This retractable housing has a similar design based on 25 mm port couplings and O-rings, but it differs in that the sensor shaft is retracted further back into the chamber and it has multiple inlets and outlets for cleaning and sterilization agents. However, information from independent tests show that while drainability of steam condensate was better, the interior chamber of the retractable holder could still not be effectively sterilized or cleaned. Moreover, this retractable holder does not provide a flush in-vessel surface with the inside surface of the vessel to facilitate vessel cleaning.
Another alternative design is to use a retractable holder which requires a process connection that is much wider than the defacto standard 25 mm port connection, for example, the Endress+Hauser type CPA465-F retractable holder (xe2x80x9cCPA465-Fxe2x80x9d). The CPA465-F provides enough room for all internal surfaces of the chamber and the process wetted sensor shaft to be adequately reached for cleaning and sterilization. The wider body process connection allows steam and cleaning agents to reach all the way down to the sensor and the back of the probe seal. Up to this point the CPA465-F has been available with industry standard process connections including the 2 inch TRI-CLAMP(trademark), APV(trademark) and VARIVENT(trademark) quick disconnect type fittings (see Endress+Hauser Technical literature TI 146 C/24/ae). These process connections are most ideally suited to pipeline type installation. The manufacturers of the APV(trademark) and VARIVENT(trademark) fittings have also developed sanitary design flow through chambers for use with their process connections. However, most applications require the sensor to be mounted onto a vessel wall (typically fermenters and reactor vessels). In order to mount the CPA465-F to a vessel wall using the TRI-CLAMP(trademark), APV(trademark) or VARIVENT(trademark) process connections, a nozzle would have to be welded to the side of the vessel at an angle. This is not considered preferred practice for sanitary applications as such nozzles cannot be cleaned easily and disturb the laminar flow often required for ideal mixing within the vessels. A flush mount construction approach is preferred.
Thus, there is a need for a retractable holder and process connection that has an effective cleaning and/or sterilization path for wetted parts of the sensor and retractable holder while also being capable of a substantially flush mounting with the interior wall of a vessel for cleaning and/or sterilization of the interior surface of the vessel.
In one embodiment, the present invention provides an apparatus for holding a sensor for sensing the contents of a vessel that has a wall. The apparatus has an extended position where the sensor is exposed to the contents of the vessel and a retracted position for cleaning and/or sterilization of the sensor. The apparatus includes a process connection configured to connect the apparatus to the wall of the vessel. The process connection defines an aperture including a first rim, a second rim angularly displaced from the first rim, and a sidewall extending between the first rim and the second rim. The sidewall is angularly displaced from the first rim by no less than 135 degrees.
In an alternative embodiment, the present invention provides a process connection for connecting a sensor holder to an opening in a wall of a vessel. The process connection includes a connector configured to be coupled to the sensor holder and further configured to be coupled to the wall of the vessel. The connector defines an aperture including a first rim, a second rim angularly displaced from the first rim, and a sidewall extending between the first rim and the second rim. The sidewall is angularly displaced from the first rim by no less than 135 degrees.
The retractable holder and process connection of the present invention incorporate the advantages of the wide body retractable holder with the benefits of a substantially flush mount process connection. In addition, it improves calibration accuracy via improved flow through the xe2x80x9ccleaningxe2x80x9d chamber, which also sometimes functions as a calibration chamber. The more complete ingress of calibration fluids (buffers), as well as proper rinsing out of other fluids (buffers of different pH value) prior to calibration improves calibration. Further it facilitates better rinse out/blow out of fluids prior to re-introducing the sensor to the process. This results in a retractable holder that provides repeatable and effective cleaning and/or sterilization of the sensor and the holder, while also providing for effective cleaning and/or sterilization of the vessel.
The retractable holder and process connection of the present invention addresses the requirements for sanitary operation. It has a retractable design that can be moved between an extended measuring position and a retracted, cleaning position either manually or automatically. It provides a steam sterilizable chamber containing the sensor when the retractable holder is in the retracted, cleaning position. It provides a substantially flush process connection with the interior of the vessel providing a cleanable process connection on the interior of the vessel.
The holder enables a sensor, for example a pH, ORP, Conductivity, Turbidity or Dissolved oxygen sensor, to be manually or automatically retracted from a sanitary vessel, to be serviced (cleaned/buffered) or replaced. The new or serviced sensor can then be effectively steam sterilized and be re-inserted into the vessel without contaminating the vessel. The process connection is optimally designed to facilitate its ease of cleaning and sterilization so that the process wetted components of the holder can be effectively cleaned and steamed in place while the vessel is undergoing clean-in-place and sterilization-in-place cycles.
These features, among others, make the present invention a viable solution for users who are looking for a product that allows sensors to be inserted (manually or automatically) into a sterile environment (without contamination occurring), while providing a process connection that is also easily cleaned and sterilized from the tank side. No hard to clean nozzles are needed that will disturb the laminar flow profile within tank. The flush connection ensures that the full stroke of the holder is available for insertion into the tank away from possible skin effects that may cause un-homogeneous samples.
Additional objects, advantages and novel features of the invention are set forth in the description that follows, and will become apparent to those skilled in the art upon reviewing the drawings and the following description.